698 



MANUAL OF PHYSIOLOGY. 



The aortic bulb is continuous with two vessels which run on 

 either side of the primitive pharynx ; these are the aortse, and 

 from each of them a large branch is given off. These omphalo- 

 mesenteric arteries pass to the yelk sack, and there become split 

 up into a number of small vessels, the blood from them being 



FIG. 287. 



vil. 



Diagram of the vascular system of a human foetus. (Huxley.) #. Heart. T.A. Aortic 

 trunk, c. Common carotid artery, c'. External carotid artery, c". Internal carotid 

 artery, s. Subclavian artery, v. Vertebral artery. 1, 2, 3, 4, 5. Aortic arches. A'. 

 Dorsal aorta. 1. Omphalo-mesenteric artery, dv. Vitelline duct. o'. Omphalo-mesen- 

 teric vein. v'. Umbilical vesicle, vp. Portal vein. L. Liver, uu. Umbilical arteries. 

 u" u". Their endings in the placenta, u'. Umbilical vein. Dv. Ductus venosus. vfi. 

 Hepatic vein. cv. Vena cava inferior, vil. Iliac veins, az. Vena azygos. vc. Posterior 

 cardinal vein. DC. Duct of Cuvier. P. Lungs. 



returned partly by corresponding omphalo-mesenteric veins, 

 partly by a large vein running round the periphery of the vas- 

 cular area known as the sinus terminalis. The sinus terminalis 

 opens partly into the right and partly into the left omphalo-rnes- 

 enteric veins, the omphalo-mesenteric veins themselves subse- 



